The present invention relates generally to filtering devices and systems which can be used when an interventional procedure is being performed in a stenosed or occluded region of a blood vessel to capture embolic material that may be created and released into the bloodstream during the procedure. The embolic filtering devices and systems of the present invention are particularly useful when performing balloon angioplasty, stenting procedures, laser angioplasty or atherectomy in critical vessels, particularly in vessels such as the carotid arteries, where the release of embolic debris into the bloodstream can occlude the flow of oxygenated blood to the brain or other vital organs, which can cause devastating consequences to the patient. While the embolic protection devices and systems of the present invention are particularly useful in carotid procedures, the inventions can be used in conjunction with any vascular interventional procedure in which there is an embolic risk.
A variety of non-surgical interventional procedures have been developed over the years for opening stenosed or occluded blood vessels in a patient caused by the build up of plaque or other substances on the wall of the blood vessel. Such procedures usually involve the percutaneous introduction of the interventional device into the lumen of the artery, usually through a catheter. In typical carotid PTA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral artery and advanced through the vasculature until the distal end of the guiding catheter is in the common carotid artery. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient""s carotid vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
Another procedure is laser angioplasty which utilizes a laser to ablate the stenosis by super heating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed blood vessel in which cutting blades are rotated to shave the deposited plaque from the arterial wall. A vacuum catheter is usually used to capture the shaved plaque or thrombus from the blood stream during this procedure.
In the procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent is crimped tightly onto the balloon portion of the catheter and transported in its delivery diameter through the patient""s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, as described above, through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a collapsed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such stents manufactured from expandable heat sensitive materials allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent.
The above non-surgical interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem which can become associated with all of these non-surgical procedures, namely, the potential release of embolic debris into the bloodstream that can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient""s vascular system. Pieces of plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. Additionally, while complete vaporization of plaque is the intended goal during a laser angioplasty procedure, quite often particles are not fully vaporized and thus enter the bloodstream. Likewise, not all of the emboli created during an atherectomy procedure may be drawn into the vacuum catheter and, as a result, enter the bloodstream as well.
When any of the above-described procedures are performed in the carotid or arteries, the release of emboli into the circulatory system can be extremely dangerous and sometimes fatal to the patient. Debris that is carried by the bloodstream to distal vessels of the brain can cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although cerebral percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.
Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system following vessel treatment utilizing any one of the above-identified procedures. One approach which has been attempted is the cutting of any debris into minute sizes which pose little chance of becoming occluded in major vessels within the patient""s vasculature. However, it is often difficult to control the size of the fragments which are formed, and the potential risk of vessel occlusion still exists, making such a procedure in the carotid arteries a high-risk proposition.
Other techniques which have been developed to address the problem of removing embolic debris include the use of catheters with a vacuum source which provides temporary suction to remove embolic debris from the bloodstream. However, as mentioned above, there have been complications with such systems since the vacuum catheter may not always remove all of the embolic material from the bloodstream, and a powerful suction could cause problems to the patient""s vasculature. Other techniques which have had some limited success include the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. However, there have been problems associated with filtering systems, particularly during the expansion and collapsing of the filter within the body vessel. If the filtering device does not have a suitable mechanism for closing the filter, there is a possibility that trapped embolic debris can backflow through the inlet opening of the filter and enter the blood-stream as the filtering system is being collapsed and removed from the patient. In such a case, the act of collapsing the filter device may actually squeeze trapped embolic material through the opening of the filter and into the bloodstream.
Many of the prior art filters which can be expanded within a blood vessel are attached to the distal end of a guide wire or guide wire-like tubing which allows the filtering device to be placed in the patient""s vasculature when the guide wire is manipulated in place. Once the guide wire is in proper position in the vasculature, the embolic filter can be deployed within the vessel to capture embolic debris. The guide wire can then be used by the physician to deliver interventional devices, such as a balloon angioplasty dilatation catheter or a stent, into the area of treatment. When a combination of embolic filter and guide wire is utilized, the proximal end of a guide wire can be rotated by the physician, usually unintentionally, when the interventional device is being delivered over the guide wire in an over-the-wire fashion. If the embolic filter is rigidly affixed to the distal end of the guide wire, and the proximal end of the guide wire is twisted or rotated, that rotation will be translated along the length of the guide wire to the embolic filter, which can cause the filter to rotate or move within the vessel and possibly cause trauma to the vessel wall. Additionally, it is possible for the physician to accidentally collapse or displace the deployed filter should the guide wire twist when the interventional device is being delivered over the guide wire. Moreover, a shockwave (vibratory motion) caused by the exchange of the delivery catheter or interventional devices along the guide wire can ajar the deployed filtering device and can possibly result in trauma to the blood vessel. These types of occurrences during the interventional procedure are undesirable since they can cause trauma to the vessel which is detrimental to the patient""s health and/or cause the deployed filter to be displaced within the vessel which may result in some embolic debris flowing past the filter into the downstream vessels.
What has been needed is a reliable filtering device and system for use when treating stenosis in blood vessels which helps prevent the risk associated when embolic debris that can cause blockage in vessels at downstream locations is released into the bloodstream. The device should be capable of filtering any embolic debris which may be released into the bloodstream during the treatment and safely contain the debris until the filtering device is to be collapsed and removed from the patient""s vasculature. The device should be relatively easy for a physician to use and should provide a failsafe filtering device which captures and removes any embolic debris from the bloodstream. Moreover, such a device should be relatively easy to deploy and remove from the patient""s vasculature. The inventions disclosed herein satisfy these and other needs.
The present invention provides a number of filtering devices and systems for capturing embolic debris in a blood vessel created during the performance of a therapeutic interventional procedure, such as a balloon angioplasty or stenting procedure, in order to prevent the embolic debris from blocking blood vessels downstream from the interventional site. The devices and systems of the present invention are particularly useful while performing an interventional procedure in critical arteries, such as the carotid arteries, in which vital downstream blood vessels can easily become blocked with embolic debris, including the main blood vessels leading to the brain. When used in carotid procedures, the present invention minimizes the potential for a stroke occurring during the procedure. As a result, the present invention provides the physician with a higher degree of confidence that embolic debris is being properly collected and removed from the patient""s vasculature during the interventional procedure.
An embolic protection device and system made in accordance with the present invention includes an expandable filtering assembly which is affixed to the distal end of a tubular shaft member, such as a guide wire. The filtering assembly includes an expandable strut assembly made from a self-expanding material, such as nickel-titanium (NiTi) alloy or spring steel, and includes a number of outwardly extending struts which are capable of self-expanding from a contracted or collapsed position to an expanded or deployed position within the patient""s vasculature. A filter element made from an embolic capturing media is attached to the expandable strut assembly and moves from the collapsed position to the expanded position via the movement of the expandable struts. This expandable strut assembly is affixed to the guide wire in such a manner that the entire filtering assembly rotates or xe2x80x9cspinsxe2x80x9d freely on the guide wire to prevent the filtering assembly from being rotated after being deployed within the patient""s vasculature. In this manner, any accidental or intentional rotation of the proximal end of the guide wire is not translated to the deployed filtering assembly, which will remain stationary within the patient""s vasculature and, as such, the threat of trauma to the vessel wall and displacement of the filter caused by the rotation and/or manipulation of the guide wire can be virtually eliminated.
The expandable struts of the strut assembly can be biased to remain in their expanded position until an external force placed on the struts to collapse and maintain the struts in their contracted or collapsed position is removed. This is done through the use of a restraining sheath which is placed over the filtering assembly in a coaxial fashion to maintain the strut assembly in its collapsed position. The composite guide wire and filtering assembly, with the restraining sheath placed over the filtering assembly, can then be placed into the patient""s vasculature. Once the physician properly manipulates the guide wire into the target area, the restraining sheath can be retracted off of the expandable strut assembly to deploy the struts into their expanded position. This can be easily performed by the physician by simply retracting the proximal end of the restraining sheath (which is located outside of the patient) along the guide wire. Once the restraining sheath is retracted, the self-expanding properties of the strut assembly cause the struts to move radially outward away from the guide wire to contact the wall of the blood vessel. Again, as the struts expand radially, so does the filter element which will now be in place to collect any embolic debris that may be released into the bloodstream as the physician performs the interventional procedure. The filter sub-assembly could be bonded to the core wire at both distal and proximal ends of the embolic protection device. The core wire could be made from stainless steel or shaped memory biocompatible materials. The guide wire with the embolic protection device could be loaded into a delivery sheath. The delivery sheath could be torqued, steering the device into the intended vessel site.
The filtering assembly can be rotatably affixed to the guide wire by rotatably attaching the proximal end of the filtering assembly to the guide wire. The distal end of the strut assembly can move longitudinally along the guide wire and is also rotatable on the guide wire as well. This allows the strut assembly to move between its collapsed and expanded positions while still allowing the entire filtering assembly to freely rotate or xe2x80x9cspinxe2x80x9d about the guide wire. This attachment of the proximal end of the strut assembly to the guide wire allows the restraining sheath to be retracted from the filtering assembly and permits a recovery sheath to be placed over the expanded strut assembly to move the strut assembly back to the collapsed position when the embolic protection device is to be removed from the patient""s vasculature.
The filtering assembly also may include a dampening element or member which is utilized to absorb some of the shockwave (vibratory motion) that may be transmitted along the length of the guide wire during the handling of the guide wire by the physician. Since a sudden shock to the filtering assembly can cause the filter to scrape the wall of the blood vessel or become displaced in the vessel, the dampening member acts much like a xe2x80x9cshock absorberxe2x80x9d to absorb some of the shock and prevent the transmission of the shock force to the filtering assembly. This shock can be produced via a number of way, for example, through the exchange of interventional devices along the guide wire. Also, when the restraining sheath is removed from the filtering assembly, a shockwave can be created if the self-expanding struts open too quickly. As a result of utilizing the dampening member, shock and trauma to the patient""s vasculature are minimized and the chances of displacing the filter are virtually eliminated. In one aspect of the dampening member, a helical spring is formed on the proximal end of the expandable strut assembly to provide dampening to the assembly. Other methods of obtaining dampening can be utilized, such as attaching a separately formed spring or elastomeric member to the strut assembly.
The expandable strut assembly made in accordance with the present invention may be made from a length of tubing (also known as a xe2x80x9chypotubexe2x80x9d) made from a shape memory alloy or other self-deploying material. Stainless steel or other biocompatible metals or polymers can be utilized to form the struts of the assembly. Another material is nickel-titanium (NiTi). The individual struts of the expandable strut assembly are formed on the length of hypotube by selectively removing material from the tubing to form the particular size and shape of the strut. For example, the wall of the hypotube can be laser cut with slots to form the individual struts. Small tabs can also be lazed into the tubing along the strut which can be used to hold the filter member in place. By selectively removing portions of the hypotube by a high precision laser, similar to lasers utilized in the manufacturer of stents, one can achieve a very precise and well defined strut shape and length. In one aspect of the present invention, the pattern of the material to be removed from the hypotubing can be a repeating diamond-shaped which creates a strut pattern in the form of two inverted triangles meshed together. This particular strut pattern provides greater strength along the strut where it would have a tendency to break or become weakened. Such a strut pattern also provides for a more natural bending position for each strut, allowing the expandable strut assembly to open and close more uniformly. In one particular pattern, the strut pattern requires the removal of a repeating truncated diamond pattern by laser or other means to create the shape of the strut. In this particular pattern, each strut has a relatively straight center section formed between two inverted triangles, somewhat similar to the strut pattern described above. This particular strut pattern provides an expanded center section which allows the struts to expand to a greater volume, which helps in the capture of emboli by allowing a larger filter to be placed on the strut assembly. The center section located between the two inverted triangle also provides a sufficient working area to attach the filter element onto the strut assembly. These same features can be accomplished by curved sections which have a reduced width in the center section.
The embolic protection device may also include a filtering assembly with a strut assembly which is not self-expanding, but utilizes the application of a force on the proximal and distal ends of the strut assembly to deploy and collapsed the assembly. In this particular form of the invention, the embolic protection device includes an inner shaft member and an outer tubular member which is coaxially disposed over the inner shaft member. The distal end of the expandable strut assembly can be attached to the inner shaft member with the proximal end of the strut assembly being attached to the distal end of the outer tubular member. When there is relative movement between the inner shaft member and outer tubular member, a force is created which is imparted to the expandable strut assembly to cause the struts to either contract or expand. For example, when the outer tubular member and inner shaft member are moved relative to each other to produce an inward force acting on the proximal and distal ends of the strut assembly, the force causes the expandable struts to move from the collapsed position into the expanded position. Thereafter, when the strut assembly is to be collapsed, the outer tubular member and inner shaft member can be moved relative to each other to create an outward force acting on the proximal and distal end of the strut assembly to cause the expanded struts to move back to their collapsed position. A physician easily can manipulate the proximal ends of the inner shaft member and outer tubular member to deploy and collapse the filtering assembly as needed. The filtering assembly could be self-expanding with the movement of the inner and outer members providing the means for expanding and collapsing the assembly without the need for an outer sheath.
The inner shaft member can be a guide wire which can be utilized to move the filtering assembly directly into position downstream from the lesion for capturing any embolic debris which may be released into the bloodstream. The inner shaft member could also be a elongated tubular member which has an inner lumen that can track along a guide wire once the guide wire has been maneuvered into position into the patient""s vasculature. The entire embolic protection device can then be delivered to the desired location over the guide wire using over-the-wire techniques.
The filtering element utilized in conjunction with the embolic protection device can take on many different forms as are disclosed herein. In one aspect, the filter includes a proximal cone section which expands to the diameter of the artery in which the embolic protection device is to be deployed. This proximal cone section funnels blood flow and embolic debris into a main or central filter located distal to the proximal cone section. This proximal cone may or may not provide filtering itself. Its primary function is flow direction and its ability to collapse and expand with the expandable struts of the strut assembly. A main or central filter may comprise an elongated tubular shaped member is located distal to the proximal cone section. It is integral with the distal end of the proximal cone section and provides a large filtering area that acts as a storage reservoir for holding embolic material. Ideally, it is sized so that it receives any and all of the embolic material which it is to be filtered by the embolic protection device. It includes a number of perfusion openings which allow blood to pass through but retain embolic material. The central filter may not be collapsible or expandable, but rather may be made somewhat rigid and has an outer diameter large enough to provide a storage reservoir for holding embolic material yet can be withdrawn and delivered through the particular guiding catheter utilized to deploy the embolic protection device into the patient""s vasculature. The central filter also could be made from collapsible material, but should have an outer diameter which is large enough to provide an adequate storage reservoir yet can be withdrawn through the guiding catheter as well. Although this central filter may have a substantially fixed diameter, it can also be tapered and should have an outer diameter small enough to fit through the inner diameter of the specific guiding catheter utilized to deploy the device.
As with all of the filter elements made in accordance with the present invention, the material which can be utilized includes a variety of materials such as polymeric material which is foldable and recovers elastically to aid in the capture of the emboli trapped in the filter. Other suitable materials include braided or woven bio-compatible material which can significantly filter the desired size of the embolic debris to be captured by the filter. The filter can be formed by blowing a suitable material into the proposed shape and then cutting off unwanted portions. The perfusion openings can be drilled into the material using a laser, such as an excimer laser, or by mechanically drilling and punching the openings to the desired size and shape. Laser drilling of the holes provides accuracy, quickness and the ability to drill complex hole shapes, circles, ovals and slots. Alternatively, the central filter can be made from the same or different material from the proximal cone portion and can be welded or bonded to create an integral unit.
Still another type of filter material can be utilized in accordance with the present invention which does not require the use of mechanical drilling or laser cutting to create the precise openings in the filter which allows adequate blood perfusion while capturing the desired size of embolic debris. This filtering material utilizes an open-celled microporous structure which has uniform porosity and a network-like structure which traps embolic particles. Such filtering material has the benefit of being both mechanically strong and more tear resistant while being most effective in trapping embolic debris since the particles must travel through an intricate network of patterns in order to escape through the filter. Due to the open-celled microporous structure, the probability that embolic debris will somehow escape through the structure is extremely minimal.
The method for making this open-celled microporous filtering material consists of dissolving a selected polymer into a solvent to produce a polymer/solvent solution. This polymer/solvent solution is then cast or sprayed as a film into the desired shape and thickness. For example, the film can be cast onto a cone-shaped rotating mandrel which improves the uniformity of the film thickness. Then, a non-solvent is cast or sprayed onto the film before complete evaporation of the solvent. This non-solvent induces a phase-separation of the polymer to create the microporous structures. The resulting microporous material can then be placed onto the strut assembly to create the composite emboli-catching device.
In one particular filter made in accordance with the present invention, the proximal cone includes advantageous features which help prevent the filter from slipping off the expandable strut assembly. These features also help to prevent trapped embolic debris from being squeezed out of the filter as the filter is being collapsed for removal from the patient""s vasculature. The filter may include, for example, a set of restraining straps designed to be attached to each of the proximal ends of the struts to help secure the filter onto the strut assembly. These straps can include tabs which can be wrapped around each of the struts and permanently affixed thereto utilizing a suitable adhesive. The proximal cone section of the filter may also include a number of indented flaps which cooperate to close off the inlet opening of the central filter. These indented flaps are formed on the proximal cone and move into position to cover the opening of the central filter when the proximal cone section is collapsed by the strut assembly. Therefore, the possibility that any embolic debris trapped within the deep reservoir of the central filter will be discharged through the inlet opening is greatly diminished since the opening will be closed off by these indented flaps. Likewise, the proximal cone section of the filter can also include inwardly inverting flaps located near the inlet opening of the proximal cone section which cooperate to close off the large inlet opening of the proximal cone section whenever the strut assembly is collapsed. These elements help to prevent accidental leakage of trapped embolic debris whenever the filtering assembly is collapsed for removal from the patient.
In other aspects of the present invention, variations can be made to the devices described above which enhance their performance characteristics. For example, a strut assembly can be utilized which utilizes struts having different lengths which allows greater ease in re-sheathing the expanded strut/filter assembly since the filter and struts can be incrementally introduced into the restraining sheath, rather than having the struts and filter material enter the sheath all at once. Likewise, the filter itself can be made with a proximal edge which has a scalloped pattern which helps prevent the filter material from entering into the sheath all at once. As a result, the filtering assembly can be more easily retracted by the recovery sheath and collapsed to its smaller profile when the device is to be removed from the patient""s vasculature.
Other advantages associated with the present invention include the placement of a surface coating on the strut of the strut assembly for reducing the coefficient of friction at selected areas of the strut assembly to help prevent possible embolic material from sticking to struts. Embolic debris which does not make its way into the filter and becomes xe2x80x9cstuckxe2x80x9d on proximal struts of the filter assembly can possibly be released into the bloodstream when the filter assembly is being collapsed and withdrawn from the patient""s vasculature. In one aspect, selective deposition of a slippery polymer to the proximal struts of the strut assembly can be utilized to reduce the coefficient of friction between the embolic debris and the struts. This helps allow the embolic material to be less likely to stick on a strut assembly and more likely to pass into the filter. High areas of strain of the strut assembly may cause the coating material to crack if the coating is not sufficiently elastic. Additionally, high strain regions of the device would not be coated if the coating would affect the performance of the expansion of the strut assembly. Such materials includes polyimide and PTFE coatings, which can be applied to a strut assembly without affecting the mechanical properties of the base material. In another aspect of the invention, a coating of xe2x80x9cslipperyxe2x80x9d polymer deposited on the entire strut assembly provided that the polymer was sufficiently elastic so as not to crack or affect the ability of the struts to bend throughout the device.